Brazilian President Luiz Inacio Lula da Silva may be leaving the world stage, but he still knows how to make an impact. His blunt prediction on the first day of the G20 summit in Seoul – that the world economy was headed for "bankruptcy" unless rich nations raise consumer demand rather than relying on exports to drive recovery – was a warning shot fired at Washington.

The US, which has been accused by key developing nations of attempting to deflate the dollar with a $600bn quantative easing programme, also came under fire from China. "Don't make other people take the medicine for your disease," Yu Jianhua, a director general at China's ministry of commerce, told reporters in South Korea.

At the heart of this is the nature of global imbalances. For America, growth should return by exporting more and getting people to spend at home. For many developing nations who rely on selling goods and services into richer markets, this means sacrificing themselves on the altar of US interests. It's not just big, poorer nations, that are concerned: Germany, the world's third-largest exporter, is singing the same tune as South Korea, China and Brazil.

These countries see the dollar's fall as part of a feared circle of competitive devaluations across the major economies. Yet the US can simply shrug these attacks off – as its central bank can keep printing dollars.

The result is lots of money flowing into emerging economies, which are left to face a series of difficult decisions over the influx of dollars. Deflating a series of asset bubbles is the last thing developing nations need to tackle – especially given the bigger challenges of social inclusion, food security and infrastructure spending.

But if they sit on their hands and do nothing, poorer nations face damaging their export competitiveness by letting their currencies rise. If they intervene to keep their currencies low, the risk is that they end up holding lots of worthless greenbacks. The least palatable option is the tricky policy decision to use capital controls to keep the cash out.

What this boils down to is the inability of developing nations to translate their growing economic heft into meaningful pressure on the US. It is a dramatic illustration of where real power lies in the global system. The world's "emerging" powers are still that – and will be so for many years to come. They may represent the future, but developing nations lack the diplomatic firepower to sway the world's great powers.

What the world is dealing with is a legacy of history. The rules governing global monetary reform evolved in a uni-polar world where the dollar was dominant. Today we face a multi-polar system of currencies. The features of the past created today's problems. To insulate against volatile currency flows and speculative attacks, developing nations accumulated dollars. The dollar's role as the global reserve currency encouraged unsustainable lending in the US.

But what are the rules appropriate for both the richer nations and for large emerging markets such as China, South Africa, Brazil and India? It's hard to see how a public punch-up at Seoul is going to answer that question. The G20 aspires to be a global club, steering the world economy out of a slump – and that does mean countries must consider the international picture, rather than simply their own, narrow national interest. It means not just letting the dollar sink and tempers rise in South Korea.

Perhaps the rest of the world should recognise how important the US is to the global economy – and accepting that the world's richest nation might need a helping hand. At the same time, the G20 could also think about the poorest too – by throwing open their doors to goods and services from the least developed countries. The world's biggest economies need to prove that the G20 is more than just a place to talk to each other.